When I give myself to another person, my spouse, in the marital act, I am making physically manifest the words I pledged at the alter on our wedding day. I am speaking the language of the body to affirm a promise I made through spoken language, bearing testimony to my wedding vows and making those vows incarnate. The Church teaches that a marriage is consummated only with the first act of sexual intercourse between husband and wife. Until the couple make good with their bodies on the promises they made with their lips, there is an incompleteness to their union. Only through a total exchange of persons - a mutual self gift - do two become one.
The Church, in Her wisdom, rightly teaches that the sexual act is intrinsically both unitive and procreative, refusing to divorce the two. And contrary to popular opinion, the Church's hard line stance on matters erotic stems not from an unwillingness to "modernize" or "get with the times," but from a profound recognition of the impossibility of changing God.
Herein lies the fundamental misunderstanding of non-Christians (along with many Christians) regarding Catholic sexual ethics. In our quest to modernize and our effort to redefine reality to better suit our needs and desires, we have begun to believe that everything is a social construct. As such, all truths, all reality is merely popular opinion, and as such, can (and must!) be adjusted accordingly to best suit the needs of the masses.
What we need right now is contraceptive marital sex, so we must adjust the rules. Our discomfort with violating God's law no longer indicates that perhaps we are doing wrong, but rather, that what we are doing needs to be justified and even condoned by the greater body of Christ. We are basically asking God to rethink his plans for human sexuality, and rationalizing away our feelings of guilty discomfort until He does so.
Contraceptive sex between married couples is intrinsically disordered, because it forces the body to speak a lie. For the same reason that in-vitro fertilization is disordered in its attempt to divorce the creative from the unitive, so too is the contracepted sexual act an attempt to divorce the unitive from the creative. Even when the couple is infertile biologically, whether during the infertile period of the month or because the wife is post-menopausal, any refusal of openness to life is a denial of one's wedding vows.
This is not legalism. Far from it, this is a refusal to bear false witness to the truths spoken in our marriage vows, a refusal to perjure oneself with one's own body! When I refuse my entire self to my spouse, whether through infidelity or contracepted sex, I don't hold up my end of the bargain. At the very moment I am most passionately re-presenting my marriage vows to my beloved, I am denying my entire self and invalidating the whole she-bang! Contraceptive sex is neither total nor fruitful. What we're doing physically is engaging in the act of sexual intercourse, but what we're doing spiritually and metaphysically is removing God from the equation, refusing His design, and taking matters stubbornly into our own hands, so to speak.
If I eat for the sheer pleasure of the act but vomit to avoid the natural consequences which accompany consumption of nutrients, (read: caloric intake) I am no less in violation of natural law then if my husband and I make a practice of "pulling out" pre-climax to avoid the natural consequences of intercourse. Sex, like food, is a natural good with pleasures attached. But sex, unlike food, brings us closer to God than any other physical act, as we join forces with our beloved and literally participate in the Divine in the possible creation of an immortal soul.
Every sex act which is contracepted is a refusal to invite God there, where He should be most intimately present to us. It is here we are made most like him, given the awesome ability to love so perfectly that our love creates. It's mind blowing. And it's about more than selfish pleasure, more than recreation, and more than immediate gratification, no matter how hard we wish it were otherwise.
My desire doesn't create my reality. Only one Person can make that radical claim.